Loop antenna apparatus



Aug. 21, 1945.

` w. J. PoLYDoRoFF LOOP ANTENNA ABPARA'iUs Filed March 11. 1.943 2sheets-sheet 1 .IIIIIIIIII llll Aug. 21, 1945. w. J.- PoLYDoRoFF y2,383,415

`LoP ANTENNA AFPA-@Tris l v Filed Maren l11', l1945 '2 sheets-sheet 2 toprovide antenna construction comprising a plu- Patented Aug. 21, 1945UNITED STATES lPATENT OFFICE LOOP ANTENNA APPARATUS `Wladimir J.Polydoroff, Wilmette, Ill. Application March 11, 1943, Serial No.478,748

6 Claims. (Cl. Z50-33) The invention relates to directional loopantennae and has more particular reference to improvements in theconstruction and operation of antennae of this character for improvingreception over a wide range of frequencies.

In my Patent No. 2,354,332, granted July 25, 1944, I disclose a loopantenna having coil windings in associated relation `with an elongatedcore in the form of a long cylinder composed of finely divided ironparticles. greatest use of the iron, the coils as disclosed in saidapplication have the maximum number of turns in close association withthe iron and said coil windings are spread throughout substantial- I lythe length of the elongated core. i"

An object of Vthe present invention is to improved loop antennae of thischaracter and thereby materially increase their efiiciency in thereception of radio waves. v

Another object of the present invention is to f' provide an 'improvedconstruction of directional loop antennae for use as low impedanceloops. An important advantage of this type of antenna is due to the factthat when a small inductance l..

loop is fed into a receiver through a suitable input transformer a largerange of frequencies can be covered. It has been possible to employ suchlow impedance antennae to cover the frequency range from approximately100 to 1500 kilocycles.

However, if itis desired to cover a larger frequency range another suchantenna must be employed of either more or less inductance, which secondantenna is switched on for the corresponding extended frequency range.tennae are used in close vicinity to `each other it has been found thatYthe presence of an idle loop in the I'leld of an active one causesabsorption of the energy from the said active loop, re.. sulting inconsiderablel weakening of the signal. Also the use of two coils inclose association with each other will produce deflection of the signalfrom its true direction, which effect is known as deviation.

Another object of the invention, therefore, is

rality of loop windings and which antenna construction will receiveradio Waves of high and low frequencies andwherein the absorption lossand antennae loops so that they may be continuously rotated andmaintained at right angles with respect to each other or at any desiredangular relation.

The employment of ktwo loop antennae mounted for synchronous rotation asabove described increases the weight and bulk of the system.

\ Therefore another object of the invention is to In order to make thel(lo If two such anl the deviation effect above described issubstantially eliminated.`

It has been customary to mount each antenna loop to permit rotation ofthe same in order that its directional properties may be fully utilized.In this connection, a further object of the invention is to provideapparatus for mounting two 55 advantageously use such antenna loops in acommon structure so as to provide apparatus of small physical dimensionsand which can be operated in a manner whereby the undesirable absorptioneffects and deviation are eliminated and reception over a wide range offrequencies is made possible.

With these and various other yobjects in view the invention may consistof certain novel features of construction and operation as will be morefully described and particularly pointed out in the specification,drawings and claims appended hereto.

In the drawings which illustrate an embodiment of the invention andwherein like reference characters are used to designate like parts-Figure l. is a vertical sectional view illustrating improved apparatuscoming within the invention for mounting antenna loops to eliminateundesirable absorption and deviation effects;

Figure 2 is an elevational view illustrating a parallel position of theloops which permits assembly of the streamlined cover;

Figure 3 is a sectional View showing a modiiication of the inventionwherein two loop windings are mounted in close associated relation on asingle iron core member; and

Figure 4 is a wiring diagram showing a method whereby said loop windingson the common core member may be electrically connected in parallel byremote control.

Figures 5 and 6 are elevational and end views, respectively, showing apreferred manner of electrostatically shielding the antenna loops; and

Figure 'l is a vertical sectional view through loop antenna structuresuch as employed in Figure l.

Referring more particularly to Figure 1, the apparatus disclosedincludes two separate and independent loop antennae suitably mounted forsynchronous rotation with means being provided whereby the loops aremaintained at right angles with each other at'all times. Since theillustrated embodiment is adapted to be attached to the fuselage orsimilar section of an airplane the numeral-I indicates` the shell ofsaid plane to which the apparatus is suitably fixed by any suitablemeans. For accommodating the apparatus the shell is provided with anelongated opening II and the apparatus is positioned on the exterior' ofthe shell with respect to this opening so that proper access may be hadto the interior of the apparatus and so that the operatinginstrumentalities may project therefrom to within the airplane.

The direction finding elements of the present apparatus are indicated intheir entirety by numerals I2 and I3. These comprise loop antennae whichmay be constructed in accordance with the disclosure of my Patent No.2,354,332 herein iden- CTI titled, Figure 7 illustrating one of theseveral modifications of loop antenna structure shown in said patent. Itwill be understood that veach'loop antenna may therefore include anelongated iron core 8 preferably of finely divided iron particles havingcoils 9 in close association with the core. The coils are carried by aninsulating tube I9 which encloses the ferromagnetic core. In thismodification the coils El are wound in opposite directions and areconnected in parallel to the conductors 39 which extend through thesupport I5 and electrically connect with collector rings 3S, as will befully understood as the description pro- Cedcs. Each coil and corecombination is suitably encased within a cylindrical housing I 4 whichis carried by a support I5. Each end of the housing is closed by a discI6 held in place by means of the elongated bolt Il' extending,longitudinally through the iron core and receiving the threaded nut I 8.It will be observed that each loop antenna has a right angled relationwith its associated loop antenna. This is clearly illustrated inFigure 1. In accordance with the invention this ninety degree relationof the loops with each other is maintained at all times even though theloops are mounted for rotation in order to more fully realize theirdirectional properties.

The base member of the present apparatus is indicated by numeral 20, thesame having a relatively narrow peripheral top surface 2I which is flatthroughout its extent for receiving the streamlined cover 22 of thedevice. Said cover is preferably formed of a transparent plastic orother suitable material and the same is streamlined, having a shapeclosely approximating that of a bullet to materially reduce airresistance. Said cover is thus provided with a pointed nose 23 and arounded end 24. A plurality of screws 25 are adapted to fit within therecesses 26 formed in the base member 2D to securely and releasably holdthe streamlined cover to the base.

lThe support I of each loop antenna is recessed for receiving a shaft bymeans of which the loop antenna is journaled for rotation. The loopantenna indicated by numeral I2 is xed to shaft 2l in this manner, theparts being held in proper assembled relation by the screws 28. Alsoloop antenna I3 is fixed to shaft 29 with the parts being securedtogether by the screws 3D. The shafts pass through the partition 3I todepend below the same and extend into a recess provided therefor in thebottom wall 32 of the base member. The partition and bottom walltherefore provide the necessary journalling means for each shaft. Theshafts are equipped with similar gears 33 and 34, respectively,preferably of the split type, to provide tension for eliminating backlash. Each gear is Xed to its shaft by means of the set screw 35. Theshafts are hollow to permit the passage of wires from the windings andbelow the gear each shaft is provided with an insulating sleeve havingcollector rings 36, the said rings for shaft 21 being indicated bynumeral 36 and the rings for shaft 29 being indicated by numeral 3l, towhich rings the wires from the windings are soldered. A brush 38 ismaintained in contact with each collector ring and the brushes for therings 35 are suitably supported by the upright 40, whereas, the brushesfor the collector rings 31 are fixed to the upright 4 I. By means ofsuitable wires provided by the cable 42 the brushes are electricallyconnected to apparatus inside the airplane and the electrical circuit istherefore completed by said brushes through the collector rings to therespective loop windings of the antennae I2 and I3.

l The opening II in the shell of the airplane is made large enough topermit the member 43 to pass through the same for securement to thebottom Wall 32 of the base. The screws 44 are employed to releasablysecure said member in place. The member provides a suitable opening sothat cable 42 may extend through the same into the interior of theapparatus which is necessary since the individual wires of the cablehave electrical connection with the brushes 38. The member 43 alsoprovides the boss 45 which journals the main shaft 46 of the apparatusand also the actuating shaft 41 adapted to have interlocking engagementwith shaft 46 by means of which the same is rotated. The main gear 48 isfixedI to shaft 45 and said gear in turn meshes with the split gears 33and 34. Rotation of the main gear therefore simultaneously rotates thesplit gears and their corresponding shafts. The antenna loops I2 and I3are synchronously rotated and therefore the angular relation which oneloop has with its companion loop is maintained at all times.

The loop I2 may be considered as having high inductance and loop I3 maybe'considered as having 10W inductance. Therefore in operation of thepresent apparatus the loop I2 will be placed in operation when it isdesired to pick up radio waves of low frequency and loop I3 Will beplaced in operation when it is desired to pick up high frequency radiowaves. When one loop winding is in operation the other loop winding isidle. When two such loop antennae loops in close association with eachother are operated in this manner the presence of an idle loop inthefield of an active one results in absorption of the energy from the saidactive loop, which results in weakening of the signal and is thereforeundesirable. In the apparatus of the invention this absorption loss issubstantially eliminated by placing one loop antenna at right angles toits companion loop and in maintaining this relationship while providingfor free rotation of the loops.

The split gears 33 and 34 can be easily assembled on their respectiveshafts since the operator has access to the interior of the base member29 when the member 43 is removed. The uprights `40 and 4I and thebrushes are xed to said member so that these elements in addition to thecable and the boss 45 constitute a unit. In assembling the streamlinedcover it is necessary to place the loops I2 and I3 in parallelalignment, as shown in Figure 2. Only when both loops are thus alignedis'it possible to place the elongated cover over the same. To rotateloop I3 by hand and at the same time prevent loop I2 from rotating itbecomes necessary to loosen the split gear 34 to disconnect said gearfrom shaft 29. Ihe geared relation which the two shafts have with eachother is thereby disconnected so that shaft 29 and the loop antenna I3xed thereto can be independently rotated into a longitudinal directionsimilar to that occupied by loop I2. The invention provides an opening50 in the base member 29 which is aligned with the split gear 34 so thatthe operator can insert a screw driver or other instrument through saidopening 50 and release the connection which this gear has with shaft 29.

Normally said opening D is maintained closed by means of the screw 5I.It is necessary to proceed as above indicated each time it is desired toremove the streamlined cover from the apparatus or replace said cover.

With the streamlined cover in place the split gear 34 is again securedtoits shaft 29 and the geared relation between the two loops I2 and I3is the same as before, with the result that the loops are simultaneouslyrotated by the actuating shaft 41 while desired angular relation betweenloops isl maintained. The fact that loop antenna I3 can be released fromits split gear 34 renders it possible to connect the loops through thegears in any desired angular relation from a ninety degrec relation ofthe magnetic axes of the loops to a parallel alignment, as shown inFigure 2.

In Figure 3 a modification of the invention is disclosed wherein a lowinductance loop winding and a high inductance loop winding are bothwound on the same core. Winding the two loops on a common core has theadvantage that the total weight and bulk of the system is materiallyreduced.

Referring to said ligure, the elongated core indicated by numeral 4lillis composed of finely divided iron particles. Since an iron core is usedthe effective permeability is increased. A form or shell 6I ofinsulating material is placed over the iron core, the same having aclose fit therewith and providing a plurality of recesses extendingcompletely around the cylindrical shell for receiving the wirecomprising the respective windings. The shaft 62 extends into the co-re60 substantially centrally thereof and said shaft may be suitablyjournalled to provide for rotation of the core. The two coils 63,located in the outside recesses provided by the insulating shell 5I',cornprise a plurality of turns of relatively fine wire. The coils areconnected by conductor B4 and therefore they constitute the loop of highinductance indicated by numeral 65 which is employed for the receptionof radio waves of lo-w frequency. 'Ihe conductor 84 is provided with acenter tap which is grounded at 66. The inside recesses pro- 7 vided bythe shell 6 Icontain a less number of turns of heavy Wire to form coilsB1 which therefore have low inductance and comprise the loopindicated bynumeral 88 for receiving radio waves of high frequency. The conductor 69connects the two coils -61 and said conductor is provided'with a centertap grounded at 10.

In this modication of the invention the coils 63 comprise the loop 85 ofhigh inductance and coils 81 comprise the loop 68 of low inductance.Both are wound on the same iron core to save weight and reduce the bulkof the system. However, the loops are coaxial to each other and they aretherefore subject to absorption and deviation, as previously explainedin connection with Figure l. In accordance with the invention theseundesirable eiects are substantially eliminated by the provision ofmeans for electrically connecting the high inductance loop G5 inparallel withthe low inductance loop 88 during the operation of said lowinductance loop. As a result the inductance of loop 58 is somewhatreduced but this can be compensated for by initially adding a few eX-tra turnsof wire to coils 61.

To accomplish the electrical connection of the loops for thepurposeabove described, the invention provides a plurality of collector ringsindicated by numerals] I, 12, 13, 14 and 15. The collector rings aresuitably fixed to rotate with shaft 82,' being insulated therefrom bymeans of the lsleeve 16 of insulating material.

ring has contact with a metal brush 11 collectively double'pole singlethrow switch 84. In a similar Imanner the coils 53A are electricallyconnected by conductors 85 and 86 with the collector rings 14 and 15respectively. Likewise the circuit is continued by the brushes 11 incontact with these collector rings and .by the conductors 81 and 88 tothe switch 84 previously mentioned. The conductors 99 and 9| constitutethe conductors enclosed within cable 92 which extends to within theairplane or other enclosure on which the present apparatus is mounted.The center collector ring '13 is suitably grounded at 93 and thiscollector yring through its corresponding brush 11 is connected byconductor 94 to the sheath of the cable.

During operation of the apparatus as disclosed in Figure 3 it will beunderstood that switch 84 Awill be in open position fo-r the receptionof radio waves in the low frequency range since these frequencies arepicked up by the windings 63 comprising the loop 65 of high inductance.This loop `is electrically connected at all times to the collector rings14 and-15 which in turn have connectio-n with the conductorsfrom cable92. Therefore when this loop 65 is in operation it will be understoodthat the switch 84 is open and loop BB remains idle. However, inaccordance with lthe invention the high frequency low inductance `loop88 is always operated in parallel with the low `frequency highinductance loop 65. Loop 68 hav- -ing connection with -only be'connected to conductors 90 and 9| of the cable 92 by closing the switch84. Closing of said vswitchY automatically connects the loop 65 inparcollector rings 1I andy 12 can allel` therewith.

Figure 4 discloses apparatus whereby the loops may be connected inparallel as above described by remote control. In place of the doublepole single throw switch a contactor 95 is provided which, as showninsaid figure, is normally inoperative. Therefore the conductors 82 and83v are normally disconnected from the conductors 81 and 88. Thecontactor is actuated by means of the vsolenoid 9B having electricalconnection through switch 91 with a source of current 98. When switch 91is closed the solenoid 98 is energized and contactor 95 is caused todescend into its operative position. The contactor will therefore close`the circuit to the conductors 82 and 83 leading to the coils comprisingthe loop 68 and the said loop is thus placed in operation, beingautomatically connected in parallel with the coils comprising aloop 65.Therefore whenever the high frequency loop is used it is in parallelwith the idle low frequency loop. For best results the above describedswitch structure should be placed as close to the connector rings aspossible.

In direction finding loops the direction of the transmitter is indicatedby a sharp zero signal when the loop axis points toward the transmitter.In order to obtain sharp directional bearings only the electromagneticcomponent of the radio wave Each collector shculd act on the loop, theelectrostatic component being suppressed by electrostatic shielding ofthe windings. Preferred structure for carrying out the above is shown inFigures 5 and 6 wherein the loop antenna is enclosed by special clothinto which metal wires are woven in one direction. After the coils areplaced in the insulating form 6I another insulating tube is placed overthe windings in order to protect them from the atmosphere, said tubebeing indicated in Figure 5 by numeral I 00. The cloth having the wiresIUI is then placed around the exterior surface of the tube 00 and inaccordance with the invention the cloth is provided with a gap |02 sothat the wires extending in the same direction circumferentially of theloop antenna are not joined but are left open circuited at the top.However, all the wires are electrically connected in the vicinity of thelower portion of the casing and the same is grounded at l 03. Each loopantenna is also closed at its respective ends by the disc I 04 which iscovered with cloth providing the vertically disposed wires |05. Thesewires are also electrically connected at their lower ends and whichconnection is suitably grounded at |06.

An electrostatic shield may also be made from thin metal foil or metalleaf, preferably metal such as copper, which is a good conductor ofelectricity. A gap is provided so that the metal foil does not extendcompletely around the loop antenna and also in a manner as disclosed thevarious parts of the metal shield are grounded.

The invention is not to be limited to or by details of construction ofthe particular embodiment thereof illustrated by the drawings, asvarious other forms of the device will of course be apparent to thoseskilled in the art Without departing from the spirit of the invention orthe scope of the claims.

What is claimed is:

1. An antenna system for the reception of radio waves, said systemincluding a loop antenna of high inductance for receiving radio waves oflow frequency, a second loop antenna of low inductance for the receptionof radio Waves of high frequency, each loop antenna comprising a pair ofcoils coaxially wound on an elongated core member, a shaft journallingeach said loop antenna for rotation on an axis normal to its magneticaxis, a gear on each shaft, releasable means securing one of said gearsto its shaft whereby the shaft may be independently rotated when thegear is released, and a driving gear having meshing relation with thegears fixed to the shafts respectively, said geared connection of theloops being constructed and arranged to provide for rotation of theloops simultaneously While maintaining their magnetic axes at rightangles to each other.

2. An antenna system for the reception of radio waves, said systemincluding two loops spaced a distance laterally of each other andadapted to rotate in unison, each loop comprising an iron core having atleast one coil coaxially wound on the core and in close associationtherewith, a shaft supporting each loop and journalling its loop forrotation on an axis normal to the magnetic axis of the loop, a drivingmember fixed to each shaft, and actuating means for rotating the drivingmembers simultaneously and to a like extent, whereby both loops arerotated at the same time and whereby any preset relation between themagnetic axes of the loop is maintained.

3. An antenna system for the reception of radio waves, said systemincluding two loops spaced a distance laterally of each other andadapted to rotate in unison, each loop comprising an elongated iron corehaving at least one coil coaxially wound on the core andin closeassociation therewith, a shaft supporting each loop and journalling itsloop for rotation on an axis normal to the magnetic axis of the loop, adriving gear fixed to each shaft, releasable means securing one of saidgears to its shaft whereby the loop supported by said shaft may berotated independently when the gear is released, and an actuating gearfor rotating the driving gears simultaneously and to a like extent,whereby both loops are rotated at the same time and whereby any presetangular relation between the magnetic axis of the loops is maintained.

4. An antenna system for the reception of radio waves, in combination,an elongated streamlined housing having an opening in the wall thereofintermediate the ends of the housing, supporting means for saidelongated housing having secured relation with the Wall defining saidopening in the housing, at least two loop antennae having locationwithin the streamlined housing and spaced along the longitudinal axis ofsaid housing, each loop comprising an iron core having at least one coilcoaxially wound on the core and in close association therewith, a shaftsupporting each loop and journalling its loop for rotation on an axisnormal to the magnetic axis of the loop and also normal to thelongitudinal axis of said housing, a driving member xed to each shaft,and actuating means for rotating the driving members simultaneously andto a like extent.

5. An antenna system for the reception of radio waves, in combination,an elongated streamlined housing having an opening in the wall thereofintermediate the ends of the housing, supporting means for saidelongated housing having secured relation with the Wall dening saidopening in the housing, at least two loop antennae having locationwithin the streamlined housing and spaced along the longitudinal axis ofsaid housing, a shaft supporting each loop and journalling its loop forrotation on an axis normal to the magnetic axis of the loop and alsonormal to the longitudinal axis of said housing, a driving member fixedto each shaft, and actuating means for rotating the driving memberssimultaneously and to a like extent.

6. An antenna system for the reception of radio waves as dened by claim4, wherein the supporting means for the elongated housing additionallysupports the shafts for the loops in a manner permitting rotation of thesame.

WLADIMIR J. POLYDOROFF.

